ByMary Clare Jalonick, Associated PressMay 27, 2014

First lady Michelle Obama joins a discussion with school leaders and experts surrounding school nutrition in an event in the Eisenhower Executive Office Building on the White House complex in Washington, Tuesday, May 27.

First lady Michelle Obama is striking back at House Republicans who are trying to weaken healthier school meal standards, saying any effort to roll back the guidelines is "unacceptable."

The rules set by Congress and the administration over the last several years require more whole grains in the lunch line and set limits on sodium, sugar and fat. The first lady met Tuesday with school nutrition officials who said the guidelines are working in their schools.

The event was an unusual move for the first lady, who has largely stayed away from policy fights since she lobbied for congressional passage of a child nutrition law in 2010.

An agriculture spending bill approved by a House subcommittee last week would allow schools to waive the standards if they have a net loss on school food programs for a six-month period. Rep. Robert Aderholt, R-Ala., who wrote the bill, said he was responding to requests from school food directors. The House Appropriations Committee is expected to approve the spending bill this week.

At the White House event, school nutrition directors from New York City to Los Angeles to a rural county in Georgia told the first lady success stories about implementing the standards and said they would be disappointed to see any roll backs.

"We're not just talking about food, we're talking about education," said David Binkle of the Los Angeles Unified School District. He said participation is up in his district, along with test scores and graduation rates.

The first lady asked the group for advice about how they can better respond to schools that are struggling, and suggested that the conversation should be focused on helping those schools rather than rolling back some of the standards completely. She said the government and schools can also do more to work with students to get them interested in what they are eating.

The guidelines have been phased in over the past two school years, with more changes coming in 2014. The School Nutrition Association, which represents school nutrition directors and companies that sell food to schools, has lobbied for changes to the standards.

The president of the group said Tuesday that the school nutrition officials invited to the White House aren't representative of those who have concerns.

"Our request for flexibility under the new standards does not come from industry or politics, it comes from thousands of school cafeteria professionals who have shown how these overly prescriptive regulations are hindering their effort to get students to eat healthy school meals," said SNA's Leah Schmidt.

The schools pushing for changes say limits on sodium and requirements for more whole grains are particularly challenging, while some school officials say kids are throwing away fruits and vegetables that are required.

The Agriculture Department, which administers the rules, has tweaked them along the way to try to help schools that have concerns. The department scrapped limits on the amount of proteins and grains that kids could eat after students complained they were hungry. Last week, USDA announced it would allow some schools to delay serving whole grain pastas just hours after the House subcommittee approved the opt-out language.

Not all school groups are lobbying for changes. The national PTA is pushing lawmakers to keep the standards intact.

"At a time when families are working hard to live healthy lives, school meals should be supporting families' efforts, not working against them," PTA President Otha Thornton wrote to members of Congress.